Device for illuminating a particle, and a system and a method for particle imaging

ABSTRACT

A device (110) for illuminating a particle comprises: a light waveguide (112; 412a, 412b; 512a, 512b) arranged on a substrate (114); an output coupler (118) configured to output a light beam (150; 450a, 450b; 550a, 550b) forming a sheet-like shape having a cross-section which has an extension in a first direction being larger than a size of a particle; and a fluidic channel (116; 416; 516) arranged on the substrate (114) for guiding a flow of particles along a longitudinal direction of the fluidic channel (116; 416; 516); wherein the sheet-like shape of the light beam (150; 450a, 450b; 550a, 550b) is arranged within the fluidic channel (116; 416; 516) and the first direction of the cross-section of the light beam (150; 450a, 450b; 550a, 550b) forms an angle to the longitudinal direction of the fluidic channel (116; 416; 516). A system (100) for imaging the particle comprises the device, an array (130; 430a, 430b; 530) of light-detecting elements (132; 432a, 432b; 532); and a lens (120) to converge light towards the array (130; 430a, 430b; 530) such that each light-detecting element (132; 432a, 432b; 532) detects light originating from a corresponding position in the fluidic channel (116; 416; 516).

TECHNICAL FIELD

The present inventive concept relates to a device for illuminating aparticle in a fluidic channel. The present inventive concept alsorelates to a system and a method for particle imaging.

BACKGROUND

In flow cytometry, cells are suspended in a stream of fluid which may bepassed through an electronic detection apparatus. A flow cytometer mayallow simultaneous analysis of multiple physical and chemicalcharacteristics of thousands of particles per second. Flow cytometry maytypically be used in cell counting and cell sorting. However, morphologyof cells may not be acquired in flow cytometry.

Microscopy, on the other hand, may generate images of cells and allowdetermining detailed information of cells with a higher spatialresolution than may be obtained in flow cytometry, such as determiningcell morphology. However, microscopy may be limited by a very lowthroughput of cells.

Image cytometry acquires cell images for fast flowing cells in a flowcytometer. Image cytometry is an emerging technology combiningadvantages of cell microscopy (rich information but low throughput) andconventional flow cytometry (high throughput but limited information).

However, current image cytometry techniques require either dedicated andslow imagers or complicated optical systems. As a result, the cellimaging throughput is still not sufficient for practical applications,which may require imaging of 10000 cells/s or higher. Further, thecomplicated optics involved in current systems imply that theinstruments are expensive and cumbersome to use.

An example of image cytometry is provided in Han Y., Lo Y.-H., “ImagingCells in Flow Cytometer Using Spatial-Temporal Transformation”,Scientific Reports 2015, No. 5. The method uses mathematical algorithmsand a spatial filter as the only hardware needed to give flow cytometersimaging capabilities. Instead of CCDs or any megapixel cameras found inimaging systems, high quality image of fast moving cells is obtained ina flow cytometer using photomultiplier tube detectors, thus obtaininghigh throughput in manners fully compatible with existing cytometers.

However, the set-up is still bulky and requires a number of opticalelements in a plurality of optical paths. Further, the throughput of theapplication may still need to be improved.

SUMMARY

An objective of the present inventive concept is to enable imaging ofparticles such that images with high spatial resolution may be obtained,while allowing a high throughput of particles.

These and other objectives of the present inventive concept are at leastpartly met by the invention as defined in the independent claims.Preferred embodiments are set out in the dependent claims.

According to a first aspect, there is provided a device for illuminatinga particle in a fluidic channel, the device comprising: a lightwaveguide arranged on a substrate; an output coupler configured tooutput light from the light waveguide to form a light beam, wherein thelight beam forms a sheet-like shape such that at a distance from theoutput coupler the light beam has a cross-section which has an extensionin a first direction being larger than a size of a particle; and afluidic channel arranged on the substrate for guiding a flow ofparticles through the fluidic channel along a longitudinal direction ofthe fluidic channel; wherein the light waveguide and the fluidic channelare arranged in relation to each other such that the light beam at saiddistance from the output coupler is arranged within the fluidic channel,wherein the first direction of the cross-section of the light beam formsan angle to the longitudinal direction of the fluidic channel.

Thanks to the invention, there is provided a compact set-up forilluminating a particle. The set-up may be used for imaging of theparticle such that the particle may be imaged with a high spatialresolution. Furthermore, the imaging may be enabled with high throughputsuch that speed of particles through the fluidic channel may be veryhigh.

By means of the fluidic channel and the light waveguide being arrangedon the same substrate, a compact set-up for illumination is provided.The light waveguide may be formed on a substrate using semiconductorprocessing, which is suitable for mass production and enablesminiaturization to form a small-size set-up. Also, the fluidic channelmay be formed on the substrate by directly fabricating a structuredefining the fluidic channel on the substrate, or the fluidic channelbeing manufactured separately and then bonded to the substratecomprising the light waveguide.

The light beam forming a sheet-like shape implies that the light beammay selectably illuminate the particle or a portion of the particle. Thesheet-like shape may define a thickness (along a direction of flow ofparticles in the fluidic channel) which is being illuminated. Thisimplies that the illumination may select a portion in the fluidicchannel which interacts with illumination light and may hence selectthis portion for imaging.

This may be advantageously combined with an image sensor which includesone or a few rows of light-detecting elements. The image sensor doestherefore not need to read out light intensity values from a large arrayof light-detecting elements. Rather, each light-detecting element thatis to provide a light intensity value to be read out may be associatedwith its own read-out element (e.g. an analog-to-digital converter).This implies that read out of image information in terms of lightintensity detected by light-detecting elements may be performed veryquickly and hence imaging may be allowed while having a high throughputthrough the fluidic channel.

As used herein, the term “the light beam forms a sheet-like shape”should be construed as the light beam having a cross-section with asubstantially rectangular shape and which is relatively uniform in apropagation direction of the light beam through the fluidic channel. Itshould be understood that the cross-section need not be exactlyrectangular, but may be rounded at edges of the cross-section. Further,it should be understood that the cross-section need not be exactlyuniform. On the contrary, the cross-section may be slightly narrowing orslightly expanding within the fluidic channel, or even first narrowingwithin the fluidic channel towards a smallest cross-section within thefluidic channel and then expanding within the fluidic channel.

The device may be used for illuminating any kind of inorganic or organicparticles, man-made or natural particles. For example, polystyreneparticles, silicon oxide particles, metal particles, magnetic particles;biological cells, bacteria, virus, extracellular vesicles, or theaggregate of the same or different particles may be illuminated by thedevice so as to allow imaging of the particle.

According to an embodiment, the output coupler is configured to outputlight, wherein the light beam has a cross-section which has a largeextension in the first direction and a small extension in a seconddirection, the small extension being smaller than the size of aparticle.

Thanks to the light beam having a cross-section with a large extensionbeing larger than the size of the particle and a small extension beingsmaller than the size of the particle, the light beam may illuminate aslice through a particle. This implies that the illumination may selecta portion of the particle which interacts with illumination light andmay hence select this portion for imaging.

Thereby, the illumination selects the slice through the particle that isimaged during a specific point in time. The light interacting with theparticle may be transmitted onto a single or a few rows oflight-detecting elements for quickly reading light information. Thisimplies that, as the particle moves through the fluidic channel, asequence of slices of the particle may be illuminated and imaged in avery fast manner, such that the sequence of imaged slices may then forma complete image of the particle.

Thus, the device for illuminating a particle enables particle imagingwith a high spatial resolution while allowing a high throughput ofparticles. For example, in one embodiment, a 1 MHz readout from thelight-detecting elements may be used, which may allow a particle flowspeed of 0.5 m/s using a 0.5 μm resolution.

According to an embodiment, the first direction of the light beam istransverse to the longitudinal direction of the fluidic channel.

This implies that a particle flowing through the fluidic channel willpass through the light beam such that an entire cross-section of theparticle (in a direction transverse to the movement of the particle) maybe illuminated by the light beam. Hence, the entire cross-section of theparticle may be illuminated and imaged.

The light beam may be arranged such that the first direction of thelight beam extend mainly through a center of the fluidic channel. Thismay be advantageous, because if light interacts with a side wall of thefluidic channel, it may affect imaging of the particle in the fluidicchannel.

However, the first direction of the light beam need not be exactlytransverse to the longitudinal direction of the fluidic channel. Thefirst direction may illuminate a cross-section of the particle which isnot transverse to the movement of the particle.

The first direction may be configured to form an angle to thelongitudinal direction of the fluidic channel. This implies that thefirst direction should not be parallel to the longitudinal direction ofthe fluidic channel. However, if the angle between the first directionand the longitudinal direction of the fluidic channel is close to 0, thelight beam may need to have a large extension such that an entireparticle cross-section (traverse to the flow direction or longitudinaldirection of the fluidic channel) will be illuminated by the light beamwhen the particle flows through the fluidic channel. The first directionmay form an angle to the longitudinal direction of the fluidic channelin the range of 45-135°.

In other words, according to an embodiment, the extension in the firstdirection of the cross-section of the light beam extends substantiallyacross a cross-section of the fluidic channel from a first side wall ofthe fluidic channel to a second side wall of the fluidic channelopposite to the first side wall. The extension need not be transverse tothe longitudinal direction of the fluidic channel, but may form a linebetween the first and second side walls such that an entirecross-section of the particle flowing through the fluidic channel maystill be illuminated.

According to an embodiment, the light waveguide and the fluidic channelare arranged in relation to each other such that the light beam from theoutput coupler enters the fluidic channel through a light entrance wallof the fluidic channel for propagating towards a light exit wall of thefluidic channel opposite to the light entrance wall, and wherein thelight beam has a cross-section with a large extension and a smallextension throughout the fluidic channel between the light entrance walland the light exit wall.

This implies that the light beam may have a relatively uniform andsheet-like shape through an entire cross-section between the lightentrance wall and the light exit wall of the fluidic channel. Hence, aposition of the particle between the light entrance wall and the lightexit wall will not affect possibility to image the particle. Further,the light beam will not differently illuminate different “heights” (i.e.different positions in the particle in a direction of propagation of thelight beam) such that the light beam is not selective to information ata specific height in the particle. However, it should be realized thatparts of a particle at a position farther away from the output coupler(i.e. along the propagation of the light beam) may be obstructed bylight interacting with other parts of the particle before reaching suchposition.

According to an embodiment, the device further comprises a lens arrangedon the substrate, wherein the lens is configured to receive lightinduced by the light beam interacting with a particle in the fluidicchannel and converge the received light.

The lens may be configured to direct light originating from a positionin the particle towards a single point. Thus, even if light from aposition in the particle is spread over a large angle, e.g. throughinduced fluorescence which may directed to a broad range of angles, thelight may be collected by a lens and directed towards a single point.This implies that in an image plane, specific points (in whichlight-detecting elements may be placed) may correspond to specificpositions in the particle.

By arranging the lens on the substrate, a compact package comprising thelight waveguide, the fluidic channel and the lens may be provided. Also,the relation between the lens and the light waveguide and the fluidicchannel may be well-defined such that the lens will correctly convergethe received light.

However, it should be realized that a lens may be provided separatelyfrom the substrate. The lens could thus be part of an imaging set-up,wherein the lens is separately mounted. The imaging set-up may bedelivered in a pre-set equipment or may be set up by a user that is toperform imaging of particles.

According to an embodiment, the fluidic channel is arranged above thelight waveguide on the substrate and the lens is arranged above thefluidic channel.

This implies that a stack may be formed of the light waveguide, thefluidic channel and the lens. A stacked set-up may facilitatefabrication of the device, as the different parts may be formed indifferent layers on the substrate.

However, it should be realized that the light waveguide and the fluidicchannel, and possibly also the lens, may be formed on a common surfaceof the substrate, such that they are arranged in a common plane on thesubstrate. This implies that light may be output by the output couplerpropagating in the common plane and through the fluidic channel.

It should also be realized that additionally or alternatively, a lensand the light waveguide may be arranged at a common side in relation tothe fluidic channel. This implies that light back-scattered by aparticle in the fluidic channel may be detected. If fluorescence isinduced by the light beam, fluorescent light emitted generally backwardsinto a direction from which the light beam is received by the particlemay be detected. It may be possible to detect light by detectorsarranged both on an opposite side of the fluidic channel in relation tothe light waveguide and on a common side of the fluidic channel inrelation to the light waveguide.

According to an embodiment, the light waveguide is a first lightwaveguide and the output coupler is a first output coupler configured toform a first light beam and wherein the device further comprises asecond light waveguide and a second output coupler for forming a secondlight beam, which forms a sheet-like shape such that at a distance fromthe second output coupler the second light beam has a cross-section witha large extension in a first direction and a small extension in a seconddirection.

This implies that a plurality of light beams may be provided forilluminating the particles. The light beams may have differentcharacteristics for enabling acquiring more information about theparticles in imaging of the particles.

According to an embodiment, the first light waveguide is configured toguide light of a first wavelength, whereas the second waveguide isconfigured to guide light of a second wavelength different from thefirst. Thus, the particles may be imaged using different wavelengthssuch that a spectral resolution may be provided to the imaging or thatfluorescence by different substances may be induced.

According to an embodiment, the first output coupler is arranged tooutput the first light beam to enter the fluidic channel through a lightentrance wall at a first cross-section of the fluidic channel and thesecond output coupler is arranged to output the second light beam toenter the fluidic channel through the light entrance wall at a secondcross-section of the fluidic channel downstream to the firstcross-section.

This implies that the particles may be sequentially illuminated by thefirst and second light beams as the particles flow through the fluidicchannel. Hence, illumination and imaging based on the first and secondlight beams may be separate, which may facilitate set-up of bothillumination and imaging, since the light beams will not interfere witheach other and will not affect the respective imaging using the firstand second light beams.

According to an embodiment, the sheet-like shape of the first light beamis configured to illuminate a first portion of the fluidic channel andthe sheet-like shape of the second light beam is configured toilluminate a second portion of the fluidic channel, wherein the firstand second portions of the fluidic channel are disjoint.

This implies that the light induced by the first light beam and thelight induced by the second light beam are spatially separated, whichmay facilitate detecting of the induced light with a simple set-up of animager, e.g. by using a first and a second array of light-detectingelements, each array being dedicated for detecting light induced by oneof the first and the second light beam, respectively.

According to another embodiment, the sheet-like shape of the first lightbeam is tilted towards the second cross-section from the light entrancewall to a light exit wall of the fluidic channel and wherein thesheet-like shape of the second light beam is tilted towards the firstcross-section from the light entrance wall to the light exit wall of thefluidic channel, such that the first light beam and the second lightbeam will intersect at a central portion of the fluidic channel.

This implies that the first and second light beams may illuminate theparticles at a common position of the particle. Hence, the particle maybe simultaneously illuminated. Thus, compared to sequentialillumination, the particle may not have turned or otherwise changed itsorientation between the illumination using the first and the secondlight beam. Therefore, images of the particle based on the first and thesecond light beam may be more easily compared.

Different characteristics of the light of the first and second lightbeams may be used for directing light having interacted with theparticle in slightly different ways. Thus, a diffractive lens may beused with light beams of two different wavelengths in order to directlight to different positions in an image plane depending on thewavelength of light. This may enable simultaneous imaging of theparticle while being illuminated by two light beams.

According to a second aspect, there is provided a system for particleimaging; said system comprising: a device for illuminating a particleaccording to the first aspect; and an array of light-detecting elements,wherein the array of light-detecting elements is configured such thateach light-detecting element detects light originating from acorresponding position in the fluidic channel.

Effects and features of this second aspect are largely analogous tothose described above in connection with the first aspect. Embodimentsmentioned in relation to the first aspect are largely compatible withthe second aspect.

The device for illuminating a particle of the first aspect isspecifically suited to be used in a system for particle imaging. Thesystem may or may not comprise a lens which may be integrated with asubstrate of the device and may hence be considered to be part of thedevice, or may be separate from the substrate. Further, the system maycomprise an array of light-detecting elements, wherein the array isarranged in relation to the fluidic channel of the device such that eachlight-detecting element detects light originating from a specificposition in the fluidic channel. This implies that each light-detectingelement corresponds to light from a specific position and acquired lightintensities by the array of light-detecting elements may be used forimaging of the particle.

The system may be configured for holographic imaging. Thus, the array oflight-detecting elements may be configured to detect an interferencepattern based on object light being diffracted by the particle andreference light, which is not diffracted. The interference pattern maybe acquired by the array of light-detecting elements and then, theacquired interference pattern may be reconstructed in order to determinean image of the particle.

The system may be configured for in-line digital holography, wherein thereference light is based on light of the light beam that passesunaffected through the particle. In-line digital holography may beuseful, wherein a particle that is mostly transparent to light may beimaged. Thus, a large amount of light is unaffected by the object sothat an interference pattern may be formed.

The system may alternatively be configured for off-axis digitalholography. In such case, a separate light beam of reference light isconfigured to propagate in a reference path to reach the array oflight-detecting elements, wherein the reference path by-passes theparticle such that the reference beam passes unaffected by the particlethrough the reference path. The reference light beam may be based on acommon source with the light beam illuminating the particle, such thatthe object light and reference light may be mutually coherent.

In holographic imaging, there may be no need to use a lens for focusinglight. However, according to an alternative, the system may comprise alens for converging light towards the array of light-detecting elementsand for controlling origin of light reaching a light-detecting elementin the array.

Thus, according to an embodiment of the second aspect, there is provideda system for particle imaging; said system comprising: a device forilluminating a particle according to the first aspect; an array oflight-detecting elements; and a lens, which is configured to receivelight induced by the light beam interacting with a particle in thefluidic channel and converge received light towards the array oflight-detecting elements such that each light-detecting element detectslight originating from a corresponding position in the fluidic channel.

The array of light-detecting elements may further be configured toreceive light from a particular distance in relation to the lens. Thisimplies that light out of focus may be blocked so as not to reach thearray of light-detecting elements and that confocal imaging may beprovided so as to increase optical resolution and/or contrast of anacquired image.

The system may comprise a blocking element defining a narrow slit forpassing light towards the array of light-detecting elements forproviding confocal imaging. For instance, the system may comprise anopaque sheet arranged close to the array of light-detecting elements,wherein a transparent slit is provided in the opaque sheet for passinglight towards the array of light-detecting elements. According to analternative, a size of the light-detecting elements may define the lightreaching the respective light-detecting element for providing confocalimaging. Each light-detecting element may have a small extension, atleast in a direction perpendicular to a row of the array, which maycontribute to light out of focus of the lens not reaching thelight-detecting element.

The device, lens (if any) and array of light-detecting elements may bemounted in a common housing or arrangement, such that a preparedequipment with correct relations between the device, the lens (if any)and the array is provided. The prepared equipment may thus bemanufactured and delivered in a ready-to-use state to a user. However,it should be realized that the parts of the system may be deliveredand/or manufactured as separate parts and may be assembled to form asystem suited for particle imaging by an assembling party that receivesthe manufactured parts and delivers the prepared equipment or may beassembled by the end-user.

The array of light-detecting elements may be one-dimensional. Thisimplies that a row of light-detecting elements may be provided. Thelight-detecting elements in the row may e.g. be formed as charge-coupleddevice (CCD) or as complementary metal-oxide-semiconductor (CMOS) lightsensors, wherein light intensity from each light-detecting element maybe read out by corresponding circuitry, such that read-out of the row oflight-detecting elements may be very quickly performed. For instance,the read-out circuitry associated with each light-detecting element maycomprise an analog-to-digital converter for converting the acquiredlight intensity to a digital value. It is feasible that such a set-upmay reach read-out speeds of 1 MHz or more.

It should however be realized that the array of light-detecting elementsneed not necessarily be one-dimensional. For instance, two parallel rowsof light-detecting elements may be associated with read-out circuitry onopposite sides of the parallel rows, such that the two parallel rows oflight-detecting elements are arranged between two rows of read-outcircuitry.

According to an embodiment, the array of light detecting elements maycomprise a number of rows which are used for detecting lightintensities, wherein each row may be associated with correspondingread-out circuitry in order to enable fast read-out of the detectedlight intensities.

For instance, the light having interacted with a particle is a “moving”signal because cells are flowing. This implies that there may be aGaussian light distribution in the longitudinal direction along particleflow. The Gaussian light distribution may be determined using e.g. threelight-detecting elements in different rows and arranged to correspond tothree positions along the longitudinal direction of the fluidic channel.Signals acquired by these three light-detecting elements, one afteranother or simultaneously, can be used to detect the Gaussian lightdistribution so as to improve the signal reading accuracy.

Further, another advantage of having a plurality of rows oflight-detecting elements in the array is that, a first row in the arraycan be used to detect presence of a particle in the fluidic channel,which may trigger a second and/or a third row in the array to startread-out for imaging of the particle.

According to an embodiment, the system comprises a device comprising afirst light waveguide and a second light waveguide, wherein the array oflight-detecting elements is a first array and the system furthercomprises a second array of light-detecting elements, wherein the firstarray is configured to receive light induced by the first light beaminteracting with a particle in the fluidic channel and the second arrayis configured to receive light induced by the second light beaminteracting with a particle in the fluidic channel.

Each of the first and the second array may be a one-dimensional array oflight-detecting elements. However, as discussed above, the first and thesecond arrays may comprise a plurality of rows of light-detectingelements.

The light induced by the first light beam and the second light beam maybe spatially separated, e.g. by the first light beam and the secondlight beam being arranged to illuminate the fluidic channel at differentlongitudinal positions of the fluidic channel. Thus, the first and thesecond array of light-detecting elements may be spatially separated.

However, as discussed above, the first and the second light beams may bearranged to intersect at a central portion of the fluidic channel. Usinga diffractive lens and different wavelengths of light of the first andsecond light beams, the first and second arrays may still be spatiallyseparated for receiving light induced by the first and the second lightbeams, respectively. However, the first and second arrays may then bearranged very close to each other. For instance, the first and thesecond arrays may each be a one-dimensional array, which are arrangedparallel to each other and very close to each other. In such case, thefirst and second array may be associated with read-out circuitry onopposite sides of the parallel arrays, and the first and second arraysmay also be considered to physically form a single two-dimensionalarray. However, the output from each of the first and the second arraymay be separately processed in order to enable forming separate imagesbased on two different wavelengths. It should be realized that suchseparate images may later be combined as two different channels or inanother manner in a combined image.

In one embodiment, the device is configured such that the first and thesecond light beams are not simultaneously emitted. Thus, even though thefirst and the second light waveguides and output couplers are arrangedsuch that the light beams would intersect, only a single light beam isemitted at a time. Thus, the light beams may facilitate measurementsfrom a common position in the fluidic channel even if the measurementsare not performed simultaneously. It should be realized that with such aset-up a single array of light-detecting elements may be used fordetecting light induced by the first light beam and light induced by thesecond light beam.

The system may further be configured for parallel imaging of particles.Thus, a plurality of fluidic channels may be provided such that imagingof particles in the plurality of fluidic channels may be simultaneouslyperformed.

The system may thus be provided with a plurality of light waveguides,such that a light beam as described above may be output into each of theplurality of fluidic channels. The light waveguides may be associatedwith a single light source, which may input light to each of the lightwaveguides for illuminating the particles in the plurality of fluidicchannels. Alternatively, each light waveguide may be associated with aseparate light source.

The system may comprise separate arrays of light-detecting elements fordetecting light from particles in different fluidic channels. However,according to an embodiment, the system may be set up such that a singlearray of light-detecting elements is used for detecting lightoriginating from different fluidic channels.

In an embodiment, a large one-dimensional array of light-detectingelements may be provided, such that different light-detecting elementsare configured to detect light from different fluidic channels. Inanother embodiment, a two-dimensional array of light-detecting elementsmay be provided, such that different rows of the array oflight-detecting elements are configured to detect light originating fromdifferent fluidic channels. It should be realized that the array oflight-detecting elements may be configured in other manners fordetecting light from different fluidic channels.

According to an embodiment, the system further comprises a filter forremoving excitation light from the light beam and passing fluorescencelight induced by the light beam.

This implies that the system is adapted for fluorescence measurements.The filter may thus prevent any excitation light from reaching the arrayof light-detecting elements so that the excitation light would notinterfere with fluorescence light measurements.

According to an embodiment, the method further comprises a processingunit, which is configured to receive a sequence of recorded lightintensities by the array of light-detecting elements acquired while theparticle moves through the fluidic channel and to combine the receivedsequence for forming a two-dimensional image of the particle.

The array of light-detecting elements may acquire an image of a slice ora cross-section of the particle. A sequence of acquired images by thearray, such as a sequence of lines acquired by a one-dimensional array,may thus be combined by the processing unit in order to form atwo-dimensional image.

According to a third aspect, there is provided a method for particleimaging, said method comprising: illuminating a particle moving througha fluidic channel, said particle being illuminated by means of a lightbeam that forms a sheet-like shape such that at a position within thefluidic channel, the light beam has a cross-section with a largeextension in a first direction and a small extension in a seconddirection, the large extension being larger than a size of the particleand the small extension being smaller than the size of a particle;receiving light induced by the light beam interacting with a particle inthe fluidic channel by an array of light-detecting elements such thateach light-detecting element detects light originating from acorresponding position in the fluidic channel; recording a receivedlight intensity by each of the light-detecting elements in the array forforming image information of a portion of the particle.

Effects and features of this third aspect are largely analogous to thosedescribed above in connection with the first and second aspects.Embodiments mentioned in relation to the first and second aspects arelargely compatible with the third aspect.

According to this method, the sheet-like shape of the illumination lightbeam controls a portion of the fluidic channel being illuminated. Then,an array of light-detecting elements is used in order to detect lightintensities and image the portion of the fluidic channel that isilluminated. The array of light-detecting elements may allow very quickread-out, e.g. by comprising a single or a few rows. This implies that aportion of a particle may be imaged in a very fast manner. Hence, themethod allows a high flow speed through the fluidic channel whileallowing particles in the fluidic channel to be imaged.

The method may be used for holographic imaging, as discussed above,wherein the array of light-detecting elements may detect an interferencepattern based on diffracted and undiffracted light. However, accordingto an alternative, the method may be used for detecting light beingfocused by a lens towards the array of light-detecting elements.

Thus, according to an embodiment of the third aspect, there is provideda method for particle imaging, said method comprising: illuminating aparticle moving through a fluidic channel, said particle beingilluminated by means of a light beam that forms a sheet-like shape suchthat at a position within the fluidic channel, the light beam has across-section with a large extension in a first direction and a smallextension in a second direction, the large extension being larger than asize of the particle and the small extension being smaller than the sizeof a particle; receiving, by a lens, light induced by the light beaminteracting with a particle in the fluidic channel and converging thereceived light towards an array of light-detecting elements such thateach light-detecting element detects light originating from acorresponding position in the fluidic channel; recording a receivedlight intensity by each of the light-detecting elements in the array forforming image information of a portion of the particle.

According to an embodiment, the method further comprises acquiring asequence of recorded light intensities while the particle moves throughthe fluidic channel, and combining the received sequence for forming atwo-dimensional image of the particle.

Each frame (or line) read out from the array of light-detecting elementsmay provide image information for a portion of the particle. Bystitching the image information for a number of sequential frames, animage of entire particle may be formed.

The acquiring of the sequence of recorded light intensities may besynchronized with the flow speed through the fluidic channel. Thus,sequential frames (or lines) acquired by the array may representneighboring portions of the particle.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as additional objects, features and advantages of thepresent inventive concept, will be better understood through thefollowing illustrative and non-limiting detailed description, withreference to the appended drawings. In the drawings like referencenumerals will be used for like elements unless stated otherwise.

FIG. 1a is a schematic view of a system for particle imaging accordingto a first embodiment.

FIG. 1b is a schematic view of a system for particle imaging accordingto a second embodiment.

FIG. 1c is a schematic view illustrating confocal imaging in the systemfor particle imaging according to the first embodiment.

FIG. 1d is a schematic view of a blocking element for realizing confocalimaging.

FIG. 1e is a schematic view of a system for particle imaging accordingto a third embodiment using holographic imaging.

FIG. 1f is a schematic view of light beams to be used in off-axisholographic imaging.

FIG. 2 is a schematic view illustrating imaging of a cell moving througha fluidic channel.

FIGS. 3a-c are schematic views illustrating a shape of a light beam inthe fluidic channel.

FIG. 4 is a schematic view of a system for particle imaging according toa third embodiment.

FIG. 5 is a schematic view of a system for particle imaging according toa fourth embodiment.

FIG. 6 is a flowchart of a method for particle imaging.

DETAILED DESCRIPTION

Referring now to FIG. 1a , a system 100 for particle imaging will bedescribed. The system comprises a device 110 for illuminating aparticle, a lens 120 for converging light having interacted with theparticle, and an array 130 of light-detecting elements 132 for detectinga received light intensity.

The device 110 for illuminating the particle, which will be described inmore detail below, may comprise a light waveguide 112 arranged on asubstrate 114 and a fluidic channel 116, which is also arranged on thesubstrate. A flow of a fluid carrying particles may be transportedthrough the fluidic channel 116. The light waveguide 112 may be providedwith an output coupler 118 for forming a light beam out from the lightwaveguide 112 and directing the light beam towards the fluidic channel116.

The device 110 may further comprise an input coupler 119 for receivinglight into the light waveguide 112. The input coupler 119 may beconfigured to receive light from an external light source 140 and may beconfigured to couple the light from the light source 140 into the lightwaveguide 112. A mirror may be arranged beneath the input coupler 119for improving coupling of light into the light waveguide 112.

The light source 140 may be a laser, which may facilitate providing awell-defined light beam out from the light waveguide.

The light source 140 may be associated with an alignment mechanism foradjusting position and angle of the incoming light beam to the inputcoupler 119 so as to ensure that coupling loss is minimized or reduced.

The output coupler 118 may be configured such that a light beam 150 witha sheet-like shape may be formed in the fluidic channel 116. The lightbeam 150 may thus select a portion in the fluidic channel 116 which willbe illuminated.

The input coupler 119 and the output coupler 118 may each be formed by agrating. This may enable diverting light and may also facilitate shapinga light beam leaving the coupler. However, it should be realized thatthe input coupler 119 and the output coupler 118 may be formed by otherstructures. For instance, at least the input coupler 119 may be formedby a reflecting surface, which may divert light from the external lightsource 140 into the light waveguide 112.

The light beam 150 may form a sheet through the fluidic channel 116forming an angle with the longitudinal direction of the fluidic channel116. For instance, the sheet may be transverse to the longitudinaldirection of the fluidic channel 116. The sheet-like shape may have afirst direction extending between side walls of the fluidic channel suchthat the first direction defines a width of the light beam. The widthmay be larger than a size of a particle and may be arranged in a centralportion of the fluidic channel 116 between the side walls. This impliesthat the light beam 150 will not interact with side walls of the fluidicchannel, which may otherwise cause an interference with imaging of theparticles.

The illumination by the light beam 150 in the fluidic channel 116implies that particles flowing through the fluidic channel 116 will passthrough the sheet of the light beam 150 and that an entire width of theparticle (as extending between the side walls of the fluidic channel)will be illuminated by the light beam 150. The sheet of the light beam150 may also be very thin in a second direction perpendicular to thefirst direction, which may be along the longitudinal direction of thefluidic channel 116.

The thickness of the light beam 150 may thus select a cross-section ofthe particle that is imaged by the light beam 150, at an instant intime. However, it should be realized that the thickness of the lightbeam 150 may be coarser, even exceeding a size of the particle. This mayimply that the selection of the portion of the fluidic channel 116 beingilluminated is not very detailed and only a coarse imaging of theparticle may be provided, mainly allowing details along the firstdirection of the light beam 150 to be discerned.

However, in an embodiment, the sheet of the light beam 150 may besmaller than the size of the particle and in some embodiments muchsmaller than the size of the particle. This implies that the light beam150 may select a particular cross-section of the particle. Thearrangement of the light beam 150 aids in selecting a portion of theparticle that will be imaged at a point in time.

The lens 120 may be integrated with the substrate 114 on which the lightwaveguide 112 and the fluidic channel 116 is formed. According toanother embodiment, the lens 120 may be separately arranged, at adistance from the fluidic channel 116. The lens 120 may for example be amicrofabricated Fresnel lens, which may in particular be suitable forarrangement on the substrate 114. It should also be realized that thelens 120 may comprise a plurality of optical elements together forming alens system.

The lens 120 may be configured to receive light induced by the lightbeam 150 interacting with the particle in the fluidic channel 116. Thelens 120 may be configured to receive light being directed by theparticle into a relatively large solid angle. The lens 120 may furtherbe configured to converge the received light towards an image plane.Thus, light originating from a point on the particle will be focusedonto a single point on the image plane.

The array 130 of light-detecting elements 132 may be arranged in theimage plane, such that each light-detecting element 132 may receivelight from a specific point on the object. Thus, the array oflight-detecting elements 132 may provide image information so astogether form an image of the illuminated portion of particle.

The light-detecting elements 132 in the array may e.g. be formed ascharge-coupled device (CCD) or as complementarymetal-oxide-semiconductor (CMOS) light sensors, wherein thelight-detecting element 132 is configured to accumulate a charge orgenerate a voltage in relation to the received light intensity.

A representation of the received light intensity in the light-detectingelement 132 may be read out from the light-detecting element 132 using areadout circuitry 134. Each light-detecting element 132 may beassociated with corresponding circuitry dedicated to the light-detectingelement 132, such that read-out of the information in the array 130 oflight-detecting elements 132 may be very quickly performed.

The array 130 of light-detecting elements 132 may be relatively small,comprising a single row or a few rows of light-detecting elements 132.This implies that each light-detecting element 132 may be associatedwith dedicated readout circuitry 134 without compromising a neededspatial resolution of the array 130.

Thanks to the light beam 150 being arranged to select a portion in thefluidic channel 116 that is to be imaged at a specific point in time,the array 130 of light-detecting elements 132 may be configured with asimple structure so as to enable very fast readout of the imageinformation in the array 130. This also implies that a high throughputmay be used in the fluidic channel 116.

The readout circuitry 134 may be connected to a processing unit 136 forprocessing the image information acquired by the array 130. The readoutcircuitry 134 may comprise analog-to-digital converters (ADC), e.g. oneADC associated with each light-detecting element 132. Thus, theprocessing unit 136 may receive a digital representation of the detectedlight intensities, which may facilitate processing of the imageinformation.

The processing unit 136 may be implemented in hardware, or as anycombination of software and hardware. At least part of the functionalityof the processing unit 136 may, for instance, be implemented as softwarebeing executed on a general-purpose computer. The system 100 may thuscomprise one or more processing units, such as a central processing unit(CPU), which may execute the instructions of one or more computerprograms in order to implement desired functionality.

The processing unit 136 may alternatively be implemented as firmwarearranged e.g. in an embedded system, or as a specifically designedprocessing unit, such as an Application-Specific Integrated Circuit(ASIC) or a Field-Programmable Gate Array (FPGA).

The system 100 may be implemented as an analysis equipment providing apre-defined analysis set-up with the components of the system 100 beingarranged in a well-defined and pre-set relation to each other. Thisimplies that i.a. the device 110 for illuminating particles, the lens120 and the array 130 of light-detecting elements 132 may be mounted ina common housing 160 or arrangement, such that the prepared equipmentwith correct relations between the device 110, the lens 120 and thearray 130 is provided. The prepared equipment may thus be manufacturedand delivered in a ready-to-use state to a user. When the equipment isto be used, the user need only lead the fluid to be analyzed into thefluidic channel 116 in order to allow the equipment to start analysis ofparticles in the fluidic channel 116.

However, it should be realized that the system 100 may be set up by anend-user based on parts suitable to be used in the system 100. Thus, auser may receive the device 110 for illuminating a particle, with orwithout an integrated lens 120 on the substrate 114 of the device 110.The user may then use conventional optics and array 130, such as aone-dimensional array 130 of light-detecting elements 132 in order toset up the system 100 for particle imaging.

The system 100 may be used for acquiring bright field, dark field and/orfluorescence images. The set-up of the system 100 may be adapted, e.g.with regard to an angle of the light beam 150 and a filter set 170, forrespective type of imaging.

Bright field images may be taken when the illuminating light beam 150 iscollected by the lens 120 after illuminating the particle.

Dark field images may be taken when the illuminating light beam 150 istilted or the array 130 is otherwise arranged to be shifted away from apropagation direction of the light beam 150. Thus, side scattered light,not the main illuminating light beam 150, is collected by the array 130.

As for dark field imaging, a tilted illuminating light beam 150 may alsobe used for fluorescence imaging. Further, the emitted light from theparticle, converged by the lens 120, may further pass through a filter170 to remove the (scattered) excitation light component.

The filter 170 may typically be a combined notch filter and a bandpassfilter. The filter 170 may be separately arranged from the device 110,so as e.g. to be mounted in an appropriate position in the housing 160.

The filtered light may be refocused by a further lens structure (notshown) in order to properly focus the light onto the array 130 oflight-detecting elements 132.

Referring now to FIG. 1b , a system 300 may be used for acquiring lightbeing both forward-scattered and back-scattered. Also or alternatively,fluorescence light being induced in a direction above and below thefluidic channel 116 may be detected.

The system 300 may comprise a lens 320, a filter 370 and an array 330 oflight-detecting elements 332, as described above. Also, the system 300may comprise a light waveguide 312 with an output coupler 318 foroutputting a light beam 350 and a fluidic channel 316, as describedabove.

However, the system 300 may also comprise a lens 380 integrated on thesubstrate 314 and arranged below the light waveguide 312 and the fluidicchannel 316. Hence, this lens 380 and the light waveguide 312 arearranged on a common side in relation to the fluidic channel 316. Thisimplies that light emitted by a particle in the fluidic channel 316 in abackwards direction may be received and converged by the lens 380, in asimilar manner as for the lens 320 arranged on an opposite side of thefluidic channel 316 in relation to the light waveguide 312.

Further, the system 300 may also comprise a filter 382 and an array 384of light-detecting elements 386 on the substrate below the lens 380 soas to ensure that light interacting with particles in the fluidicchannel 316 in a backwards direction is detected in a similar manner asdescribed above for imaging of the particles based on backwards emittedlight.

The system 300 may further comprise a mirror 388 or other element whichmay be configured to block light being directly reflected by theparticle in the fluidic channel 316. The intensity of reflected light,e.g. of an excitation wavelength in fluorescence imaging, may be muchhigher than the light of interest for imaging the particle. Therefore,the mirror 388 may be used to prevent directly reflected light fromreaching the lens 380 and the array 384. Compared to the set-up for atop array 330, which may be arranged not to receive an excitationwavelength due to the light beam 350 being tilted in the fluidicchannel, a bottom array 384 may be arranged much closer to the fluidicchannel 316, as the array 384 may be integrated on the substrate 314.Thus, the mirror 388 may be needed in order to enable the fluorescencelight not to be drowned in a high intensity of reflected light.

The system 300 may comprise a top detector 330 and a bottom detector 384for imaging the particles in the fluidic channel 316 from two sides.

The processing unit 336 may be configured to receive image informationfrom both the arrays 330, 384 for processing the image informationacquired by the arrays 330, 384. This may be used for forming two imagesof particles or combined into a single image representation based onimage information acquired from above and below the particles.

It should be realized that the system 300 need not comprise a topdetector 330 at all and that rather only light in the backwardsdirection from the particles in the fluidic channel 316 is detected.

It should also be realized that one or more of the lens 380, the filter382 and the array 384 of light-detecting elements 386 need notnecessarily be integrated on the substrate. On the contrary, if thesubstrate is transparent, the light in the backwards direction mayescape the substrate and may allow mounting any one of the lens 380, thefilter 382 and the array 384 separately from the substrate.

Referring now to FIG. 1c , the system 100 and/or the system 300 may beset up for confocal imaging. Although illustrated here only in relationto detection of forward-scattered light, it should be realized that theconfocal imaging may also be used in relation to detection ofback-scattered light as discussed above in relation to FIG. 1b . Also oralternatively, fluorescence light being induced in a direction aboveand/or below the fluidic channel 116, 316 may be detected.

In FIG. 1c , the system 100 is illustrated in relation to a length-wisecross-section of the fluidic channel 116, which also implies that only asingle light-detecting element 132 is shown associated with theparticular cross-section shown.

The system 100 may comprise a blocking element 190 defining a narrowslit 192 for passing light towards the array of light-detecting elementsfor providing confocal imaging.

An embodiment of the blocking element 190 is shown in perspective inFIG. 1d . The blocking element 190 may be formed by a sheet in which aslit 192 is provided through which light may pass towards the array 130of light-detecting elements 132.

As illustrated in FIG. 1c , light which is out of focus of the lens 120,as illustrated by dotted lines, will be blocked by the blocking element190, whereas light from a focal point of the lens 120 will pass throughthe slit 192 to reach the light-detecting element 132, as illustrated bydashed lines. This implies that an increased optical resolution and/orcontrast may be provided by the system 100.

According to an alternative, a size of the light-detecting element 132may define the light reaching the light-detecting element 132 forproviding confocal imaging. Thus, the illustrated dimension in FIG. 1cof the light-detecting element, i.e. a size in a direction perpendicularto the row of the array 130, may be so small as to ensure that light outof focus of the lens 120 will not reach the light-detecting element 132.

Referring now to FIG. 1e , a system 700 may be used for holographicimaging. Thus, in contrast to the systems 100, 300 discussed above, thesystem 700 need not comprise any lens.

Rather, the array 730 of light-detecting elements 732 may be configuredto receive an interference pattern based on object light beingdiffracted by the particle and reference light, which is not diffracted.Thus, the array 730 of light-detecting elements 732 may acquire aninterference pattern, which may read out by the read-out circuitry 734and be provided to the processing unit 736 for reconstruction of animage of the particle based on the acquired interference pattern.

The system 700 may comprise a light waveguide 712 with an output coupler718 for outputting a light beam 750 and providing the light beam 750 ina fluidic channel 716, as described above.

As illustrated in FIG. 1e , the system 700 may provide in-line digitalholography of the particle.

Similar to the above-described embodiments of the system, the light beam750 may be formed as a focused light sheet in the fluidic channel 716.The light sheet 750 may thus define a line in which the light sheet isfocused (where a thickness of the light sheet is minimal). This line mayprovide a one-dimensional section of the particle. The particle flowingthrough the light sheet focus is thus sectioned by the light beam 750 sothat only a narrow cross-section of the particle interacts with thelight. The scattered/unscattered light from this cross section isdetected by the array 730 of light-detecting elements 732. The array 730may comprise a single row which is aligned with the light sheet suchthat the row is aligned with the focus line of the light sheet.

The same light beam 750 may provide “reference” light for forming theinterference pattern, based on the unscattered part of illuminationlight. Hence, only a single light beam 750 may be required for acquiringan interference pattern, which allows for reconstruction of an image ofthe particle. Such a configuration offers simplicity, as a single lightbeam 750 may be used.

However, according to an alternative, the system 700 may be set up foroff-axis digital holography. Thus, as illustrated in FIG. 1f , thesystem 700 may provide a separate light path for reference light. Forinstance, the light waveguide 712 may branch light into two paths andoutput a reference light beam 752, which may not interact with theparticle.

The reference beam 752 may be formed with a separate light sheet formingstructure, such as an additional output coupler in a separate branch ofthe light waveguide 712. The reference beam 752 must not interact withthe particle in the fluidic channel 716 and may provide a uniform lightdistribution on the array 730 of light. The reference beam 752 may forinstance be formed slightly outside of the fluidic channel 716 so thatit is free from interacting with particles. The reference beam 752 isalso directed to illuminate the same array 730 of light-detectingelements 732, which also receives the light from the light beam 750 thathas been scattered by the particle. Thus, an interference pattern may beacquired by the array 730 of light-detecting elements 732 based on thescattered light from the light beam 750 and the light from the referencebeam 752. The interference pattern may then be used for reconstructingan image of the particle.

Referring now to FIG. 2, the array 130 of light-detecting elements 132may be configured to acquire a sequence of recorded light intensitieswhile the particle moves through the fluidic channel 116 regardless ofwhich optical set-up is used, as discussed above in relation to FIGS.1a-f . Thus, the processing unit 136 may receive a sequence ofrepresentations of detected light intensities by the array 130. Eachrepresentation of detected light intensities, such as a frame or a lineread out from the array 130 may form a portion of an image, and theprocessing unit 136 may be configured to combine the received sequencefor forming a two-dimensional image of the particle.

As illustrated in FIG. 2 showing a top view of a cell 200 flowingthrough the fluidic channel 116 along a flow direction A, a thin lightsheet of the light beam 150 may be projected by the output coupler 118into the fluidic channel 116. The light sheet illuminates the flowingcell 200. The induced scatter signal and/or the fluorescent signal maybe converged by the lens 120 and collected by the array 130 or aninterference pattern may be collected by the array 730.

Since the light sheet is very thin, a small cell segment may beilluminated by the light sheet at an instant in time. Signal from thissmall segment is acquired by the array 130. When the array 130 isquickly and continuously read out, the whole cell 200 is imaged segmentby segment when it flows through the light sheet. Finally, the series ofsegments may be concatenated by the processing unit 136 and thus a cellimage 210 may be constructed.

As a merely illustrating example, in the embodiment using a lens 120,the high throughput and spatial resolution that may be obtained by thesystem 100 will be described. These numbers on throughput and spatialresolution should not in any way be understood as limiting features, butshould merely function as an illustration that the system 100 may enablehigh throughput of cells 200 through a fluidic channel 116 whileallowing imaging of the cells 200 with high spatial resolution.

The array 130 of light-detecting elements 132 may be a line scanner,which may be presently available. A desired size of the array 130, i.e.the number of light detecting elements 132 in the array 130 would dependon a size of a region to be imaged. For example, if the width of thelight beam 150 spans 60 μm and a spatial resolution of 0.5 μm isdesired, an array 130 including more than 120 light-detecting elements132 would be needed.

A size of the light-detecting elements 132 may need to be smaller than aresolution given by the lens system taking into account a magnification.For instance, a numerical aperture NA of the system may be determined asNA=n*sin θ, where n is a refraction index of a medium in which the lens120 works (approximately 1.5 if the lens is arranged on the substrate114) and θ is a maximal half-angle of a cone of light that can enter thelens 120, i.e. describing a range of angles of light being accepted bythe lens 120 and focused towards the array 130. Using an angle θ of π/4,the numerical aperture NA=1.5 sin(Pi/4)≈0.06.

A resolution R of the system may be expressed as R=0.61*λ/NA, where λ isa wavelength of light. With a wavelength of light of 600 nm, theresolution becomes R=0.61*(600 nm)/NA≈345.3 nm. Further, using amagnification of the system of 50, this implies that the size of thelight-detecting element may need to be maximally 17.26 μm, which is wellwithin sizes of available line scanners.

A rate at which detected light intensities should be captured and readout will depend on a flow speed through the fluidic channel 116. Highflow speed may also help to minimize image blurring as a short exposuretime is needed. For example, a line scanner may be used with a 1 MHzline scan rate. A maximum speed v allowed through the fluidic channel116 may be expressed as v=d*f where d is the distance the cell 200 maybe allowed to move between sequential lines being acquired and f is theline scan rate. Having a resolution of 0.5 μm, the distance d thus is0.5 μm and the maximum speed v=0.5 μm*1 MHz=0.5 m/s flow speed throughthe fluidic channel 116. This may correspond to a throughput of 10000cells/s, depending on cell size.

However, a lower flow speed may help to improve signal quality.Therefore, the flow speed may need to be chosen balancing imagingsensitivity and clarity.

Referring now to FIGS. 3a-c , the light beam 150 will be furtherdescribed. The output coupler 118 is designed such that a thin lightsheet, as shown in FIG. 3a , is formed to illuminate passing cells 200in the fluidic channel 116. The light sheet may be very thin (e.g. 0.5μm) at a location in the fluidic channel 116 where the cell 200 isilluminated. The light beam 150 may have a sheet-like shape extending ina certain height and width range, e.g. each of the height and width sizeexceeding 1.5× a diameter of the cell 200. Within the sheet-like shape,the light beam may be very thin.

Referring to FIG. 3b , showing a side view of the fluidic channel 116,the height of the sheet-like shape of the light beam 150 refers to anextension between a light entrance wall and a light exit wall of thefluidic channel 116. If the fluidic channel 116 is arranged on the lightwaveguide 112, the light entrance wall will be a bottom wall of thefluidic channel 116 and the light exit wall will be a top wall of thefluidic channel 116. However, if the light waveguide 112 and the fluidicchannel 116 are formed on a common surface, the light entrance and thelight exit walls may be opposing side walls of the fluidic channel 116.

The light beam 150 may be tilted in relation to the fluidic channel 116,such that a propagation direction of the light beam 150 from the lightentrance wall to the light exit wall of the fluidic channel 116 is notalong a normal of the light entrance wall or the light exit wall,respectively, as illustrated by angle α in FIG. 3b . If the angle αdiffers from 0°, the light beam 150 may be directed away from reachingan array 130, which may be beneficial in that detected light is notdrowned in a high intensity of direct light from the light beam 150. Inan embodiment, the angle α may be in a range of 0-45°.

Referring to FIG. 3c showing a top view of the fluidic channel 116, thewidth of the sheet-like shape of the light beam 150 refers to anextension between the walls of the fluidic channel 116 which are not thelight entrance wall and the light exit wall. The light beam 150 may havea width such that an entire segment or cross-section of the cell 200will be illuminated by the light beam 150 when the cell 200 passes thelight beam 150.

The width of the sheet-like shape of the light beam 150 may extendperpendicular to the flow direction in the fluidic channel. However, thewidth need not necessarily be transverse or perpendicular to the flowdirection A, but may form an angle R, e.g. in the range of 45-135°, tothe longitudinal direction of the fluidic channel 116. If the angle βdiffers from 90°, the light beam 150 may also be directed away fromreaching the array 130, which may be beneficial in that detected lightis not drowned in a high intensity of direct light from the light beam150.

The light beam may be arranged such that the width of the light beam 150extend in a central portion of the fluidic channel 116. Thus, the lightbeam 150 may not illuminate a portion of the fluidic channel 116 closeto side walls, i.e. the walls of the fluidic channel 116 which are notthe light entrance wall and the light exit wall. This may beadvantageous, because if light interacts with a side wall of the fluidicchannel 116, it may affect imaging of the particle in the fluidicchannel 116.

Further, the sheet-like shape of the light beam 150 may have a thicknessin a direction perpendicular to the width and the height of the lightbeam 150. The thickness of the light beam 150 may be substantially alongthe flow direction in the fluidic channel 116 (depending on the angle (3between the width and the longitudinal direction of the fluidic channel116) and may thus define a thickness of a segment of the cell 200 beingimaged at a time.

It should be realized that the thickness of the light beam 150 may berelatively thick, e.g. even larger than a diameter size of the cell 200,such as up to several times the diameter size of the cell 200. This maye.g. be combined with a one-dimensional array 130 or an array 130 havingvery few rows, which may ensure that only a segment of the cell 200 isimaged at a time. However, a quality of imaging may be reduced due tointerference of light from adjacent segments of the cell 200 (not to beimaged) reaching the light-detecting elements 132. As an alternative, arelatively thick light beam 150 may be used for providing a relativelycoarse imaging of the cell 200 in a flow direction of the fluidicchannel 116.

Multi-color fluorescence images may be desirable for cell imaging, whichmay be achieved using multiple excitation wavelengths with same or alarger amount of emission wavelengths.

Referring now to FIG. 4, a system 400 will be described, which may beused for multi-color fluorescence imaging. However, the system 400 maybe used for any type of imaging, wherein plural light beams are used.

The system 400 comprises a first light waveguide 412 a and a secondlight waveguide 412 b. The light waveguides may each have an inputcoupler and an output coupler and may be associated with two differentexternal light sources. The external light sources may provide light ofdifferent wavelengths, such that the first light waveguide 412 a mayoutput a first light beam 450 a of a first wavelength and the secondlight waveguide 412 b may output a second light beam 450 b of a secondwavelength, different from the first wavelength. Each of the light beams450 a, 450 b may form a sheet-like shape as discussed above for thelight beam 150.

According to one embodiment, the system 400 may be configured forspatially differentiated excitation of particles in the fluidic channel416. The two light beams 450 a, 450 b are arranged to be parallel and toilluminate different portions of the fluidic channel 416 along thelongitudinal direction of the fluidic channel 416.

If the light beams 450 a, 450 b are arranged sufficiently close to eachother, the same lens 420 (if a lens is used) may be shared forprojecting the light induced by the light beams 450 a, 450 b interactingwith particles to the image plane.

Since the two light beams 450 a, 450 b illuminate a particle at twodifferent places along the fluidic channel 416, the array oflight-detecting elements may need to comprise a first array 430 a oflight-detecting elements 432 a and a second array 430 b oflight-detecting elements 432 b. Each of the arrays 430 a, 430 b maycomprise e.g. a one-dimensional array and may be configured in anymanner as discussed above for the array 130.

The first array 430 a may thus detect light induced by the first lightbeam 450 a and the second array 430 b may thus detect light induced bythe second light beam 450 b. The arrays 430 a, 430 b may be configuredto output image information to a common processing unit 436 or to twodifferent processing units each processing information from a singlearray 430 a, 430 b. The image information acquired by the two arrays 430a, 430 b may be combined into a single image, e.g. as two differentcolor channels within the single image.

Referring now to FIG. 5, another system 500 will be described, which maybe used for multi-color fluorescence imaging. However, the system 500may be used for any type of imaging, wherein plural light beams areused.

The system 500 also comprises a first light waveguide 512 a and a secondlight waveguide 512 b. The light waveguides may each have an inputcoupler and an output coupler and may be associated with two differentexternal light sources. The external light sources may provide light ofdifferent wavelengths, such that the first light waveguide 512 a mayoutput a first light beam 550 a of a first wavelength and the secondlight waveguide 512 b may output a second light beam 550 b of a secondwavelength, different from the first wavelength. Each of the light beams550 a, 550 b may form a sheet-like shape as discussed above for thelight beam 150.

The system 500 may be configured for excitation of particles in thefluidic channel 516 in a common position in the fluidic channel 516. Thetwo light beams 550 a, 550 b are arranged to be tilted towards eachother from spatially separate light waveguides 512 a, 512 b, such thatthe light beams 550 a, 550 b will intersect each other, e.g. in acentral part of the fluidic channel 516 between the light entrance walland the light exit wall.

Since the excitation of the particle takes place at a common position inthe fluidic channel 516, the light induced by the light beams 550 a, 550b may be projected by the lens 520 to the same place in the image plane.

This implies that a single array 530 of light-detecting elements 532 maybe sufficient in order to detect the light induced by the light beams550 a, 550 b.

Regardless of whether the system 400 or the system 500 is used, sincemultiple emission wavelengths may be projected towards the array(s) 430a, 430 b; 530 of light-detecting elements, multi-color filters 470; 570may be needed to remove an excitation wavelength component and in orderto separate the emission light beams.

The emission light beams to be detected by the array(s) 430 a, 430 b;530 of light-detecting elements may be separated in either space ortime. With a diffractive lens, emission light of different wavelengthscan be projected towards different angles and finally detected bydifferent arrays of light-detecting elements. Thus, a diffractive lensmay be used in the system 500 in order to separate the emission lightbeams induced by the light beams 550 a, 550 b and enable separatelydetecting the emission light beams in the same array (having dedicatedrows for each of the emission light beams) or even in different arrays.

Alternatively, classical beam splitting techniques can also be employedto project the multi-color emission lights to different arrays.

According to another embodiment, excitation light beams 550 a, 550 b maybe separated in time domain. The separation in time may be synchronizedwith filtering and detection of the emission beams by the array oflight-detecting elements.

For example, switching between multiple color filters may be performedvery quickly when the multiple color filters are mounted on a spin disk.A color filter switching signal may trigger both output of the multiplelight beams 550 a, 550 b to toggle on/off and the array 530 oflight-detecting elements 532 to detect light. The switching on/off ofexcitation light may e.g. be realized by a pulsed laser, or by amicroelectromechanical system mirror or an acoustic modulator.

The system according to any of the embodiments described above mayfurther be configured for parallel imaging of particles. Thus, aplurality of fluidic channels may be provided such that imaging ofparticles in the plurality of fluidic channels may be simultaneouslyperformed.

Thus, a plurality of identical systems may be provided on a commonsubstrate. Each system may be separate for particle imaging in arespective fluidic channel.

The system may thus be provided with a plurality of light waveguides,such that a light beam as described above may be output into each of theplurality of fluidic channels.

However, rather than being separate systems on a common substrate, thelight waveguides (for different fluidic channels) may be associated witha single light source, which may input light to each of the lightwaveguides for illuminating the particles in the plurality of fluidicchannels.

The system may comprise separate arrays of light-detecting elements fordetecting light from particles in different fluidic channels. However,according to an embodiment, the system may be set up such that a singlearray of light-detecting elements is used for detecting lightoriginating from different fluidic channels.

In an embodiment, a large one-dimensional array of light-detectingelements may be provided, such that different light-detecting elementsin the array are configured to detect light from different fluidicchannels. In another embodiment, a two-dimensional array oflight-detecting elements may be provided, such that different rows ofthe array of light-detecting elements are configured to detect lightoriginating from different fluidic channels. It should be realized thatthe array of light-detecting elements may be configured in other mannersfor detecting light from different fluidic channels.

Referring now to FIG. 6, a method for particle imaging will bedescribed. The method may be performed using any of the systems 100,300, 400, 500, 700 described above.

The method comprises illuminating 602 a particle moving through afluidic channel. The particle is illuminated by means of a light beamthat forms a sheet-like shape as described above. Thus, the illuminatingof the particle may select a segment of the particle which is beingilluminated and hence may be imaged at a point in time.

The method further comprises receiving 604, light induced by the lightbeam interacting with the particle in the fluidic channel by an array oflight-detecting elements. The light may or may not pass a lens, whichmay converge the received light towards an array of light-detectingelements such that each light-detecting element detects lightoriginating from a corresponding position in the fluidic channel.

The method further comprises recording 606 a received light intensity byeach of the light-detecting elements in the array for forming imageinformation of a portion of the particle.

Each of the light-detecting elements may be associated with readoutcircuitry such that the light intensities detected by thelight-detecting elements may be read out in a very fast manner. Thanksto the illuminating by the light beam being arranged to select a portionin the fluidic channel that is to be imaged at a specific point in time,the array of light-detecting elements may be configured with a simplestructure so as to enable very fast readout of the image information inthe array.

Hence, a segment of a particle may be imaged at a point in time and themethod may allow a high flow speed in the fluidic channel while stillallowing each sequential segment of the particle passing the light beamto be imaged by the array. This also implies that a high throughput maybe used in the fluidic channel.

The method may further comprise acquiring 608 a sequence of recordedlight intensities while the particle moves through the fluidic channel.

Also, the method may comprise combining 610 an acquired sequence ofrecorded light intensities. Each set of recorded light intensities inthe sequence may correspond to image information representing a segmentof the particle. Thus, by combining the acquired sequence of recordedlight intensities a two-dimensional image of the particle may be formed.

In the above the inventive concept has mainly been described withreference to a limited number of examples. However, as is readilyappreciated by a person skilled in the art, other examples than the onesdisclosed above are equally possible within the scope of the inventiveconcept, as defined by the appended claims.

For instance, although the device for illuminating a particle isdescribed having one or two light waveguides, it should be realized thateven further light waveguides may be used, wherein each light waveguidemay be configured to output a unique wavelength. The light waveguidesmay be used for providing light beams separated in space or in timedomain.

The invention claimed is:
 1. A device for illuminating a particle in afluidic channel, the device comprising: a light waveguide arranged on asubstrate; an output coupler configured to output light from the lightwaveguide to form a light beam, wherein the light beam forms asheet-like shape such that at a distance from the output coupler thelight beam has a cross-section which has an extension in a firstdirection being larger than a size of a particle; and a fluidic channelarranged on the substrate for guiding a flow of particles through thefluidic channel along a longitudinal direction of the fluidic channel;wherein the light waveguide and the fluidic channel are arranged inrelation to each other such that the light beam at said distance fromthe output coupler is arranged within the fluidic channel, wherein thefirst direction of the cross-section of the light beam forms an angle tothe longitudinal direction of the fluidic channel.
 2. The deviceaccording to claim 1, wherein the output coupler is configured to outputlight, wherein the light beam has a cross-section which has a largeextension in the first direction and a small extension in a seconddirection, the small extension being smaller than the size of aparticle.
 3. The device according to claim 1, wherein the firstdirection of the light beam is transverse to the longitudinal directionof the fluidic channel.
 4. The device according to claim 1, wherein theextension in the first direction of the cross-section of the light beamextends substantially across a cross-section of the fluidic channel froma first side wall of the fluidic channel to a second side wall of thefluidic channel opposite to the first side wall.
 5. The device accordingto claim 1, wherein the light waveguide and the fluidic channel arearranged in relation to each other such that the light beam from theoutput coupler enters the fluidic channel through a light entrance wallof the fluidic channel for propagating towards a light exit wall of thefluidic channel opposite to the light entrance wall, and wherein thelight beam has a cross-section with a large extension and a smallextension throughout the fluidic channel between the light entrance walland the light exit wall.
 6. The device according to claim 1, wherein thedevice further comprises a lens arranged on the substrate, wherein thelens is configured to receive light induced by the light beaminteracting with a particle in the fluidic channel and converge thereceived light.
 7. The device according to claim 1, wherein the lightwaveguide is a first light waveguide and the output coupler is a firstoutput coupler configured to form a first light beam and wherein thedevice further comprises a second light waveguide and a second outputcoupler for forming a second light beam, which forms a sheet-like shapesuch that at a distance from the second output coupler the second lightbeam has a cross-section with a large extension in a first direction anda small extension in a second direction.
 8. The device according toclaim 7, wherein the first output coupler is arranged to output thefirst light beam to enter the fluidic channel through a light entrancewall at a first cross-section of the fluidic channel and the secondoutput coupler is arranged to output the second light beam to enter thefluidic channel through the light entrance wall at a secondcross-section of the fluidic channel downstream to the firstcross-section.
 9. The device according to claim 7, wherein thesheet-like shape of the first light beam is tilted towards the secondcross-section from the light entrance wall to a light exit wall of thefluidic channel and wherein the sheet-like shape of the second lightbeam is tilted towards the first cross-section from the light entrancewall to the light exit wall of the fluidic channel, such that the firstlight beam and the second light beam will intersect at a central portionof the fluidic channel.
 10. A system for particle imaging; said systemcomprising: a device for illuminating a particle according to claim 1;and an array of light-detecting elements; wherein the array oflight-detecting elements is configured such that each light-detectingelement detects light originating from a corresponding position in thefluidic channel.
 11. The system according to claim 10, wherein thesystem comprises a device, wherein the light waveguide is a first lightwaveguide and the output coupler is a first output coupler configured toform a first light beam and wherein the device further comprises asecond light waveguide and a second output coupler for forming a secondlight beam, which forms a sheet-like shape such that at a distance fromthe second output coupler the second light beam has a cross-section witha lame extension in a first direction and a small extension in a seconddirection, wherein the array of light-detecting elements is a firstarray and the system further comprises a second array of light-detectingelements, wherein the first array is configured to receive light inducedby the first light beam interacting with a particle in the fluidicchannel and the second array is configured to receive light induced bythe second light beam interacting with a particle in the fluidicchannel.
 12. The system according to claim 10, further comprising afilter for removing excitation light from the light beam; and passingfluorescence light induced by the light beam.
 13. The system accordingto claim 10, further comprising a processing unit, which is configuredto receive a sequence of recorded light intensities by the array oflight-detecting elements acquired while the particle moves through thefluidic channel and to combine the received sequence for forming atwo-dimensional image of the particle.
 14. A method for particleimaging, said method comprising: illuminating a particle moving througha fluidic channel, said particle being illuminated by means of a lightbeam that forms a sheet-like shape such that at a position within thefluidic channel, the light beam has a cross-section with a largeextension in a first direction and a small extension in a seconddirection, the large extension being larger than a size of the particleand the small extension being smaller than the size of a particle;receiving, light induced by the light beam interacting with a particlein the fluidic channel by an array of light-detecting elements such thateach light-detecting element detects light originating from acorresponding position in the fluidic channel; recording a receivedlight intensity by each of the light-detecting elements in the array forforming image information of a portion of the particle.
 15. The methodaccording to claim 14, further comprising acquiring a sequence ofrecorded light intensities while the particle moves through the fluidicchannel, and combining the received sequence for forming atwo-dimensional image of the particle.